The site at Cornacarrow occupies one of those low, whale-backed hills left behind by retreating glaciers, and whoever chose it knew what they were doing: from the top, Lough Egish opens out roughly two hundred metres to the north, offering both a view and a water source that would have made the position worth defending.

The enclosure is roughly oval, measuring about forty metres east to west and thirty-five metres north to south, and is defined by a grass-covered earthen bank with an outer fosse, the fosse being a defensive ditch dug around the perimeter to reinforce the bank. Two gaps interrupt the circuit: one on the west side, with a base width of about 1.6 metres, and a wider opening on the east-south-east, measuring 2.5 metres at the base, which is thought to be the original entrance. Earthen ring forts of this kind, known in Irish as raths, were among the most common settlement forms in early medieval Ireland, typically enclosing a farmstead and its immediate household. What makes Cornacarrow slightly more arresting is what sits just outside the fosse on the south-west side: a large cist. A cist is a stone-lined burial box, usually associated with prehistoric interment, and its presence immediately adjacent to the fort raises questions that the ground does not easily answer. Whether the cist predates the earthwork entirely, or whether the two features are in some way connected, is not recorded. The juxtaposition of a burial feature and a domestic enclosure is not unique in the Irish landscape, but it gives this particular drumlin-top a layered quality that goes beyond a straightforward ring fort.